M. Okunishi

Infrared diode laser spectroscopy of the allyl radical. The ν11 band

Allyl radicals were generated by the photolysis of 1,5‐hexadiene at 193 nm and were detected by observing the ν11, i.e., CH2 symmetric wagging band by infrared diode laser kinetic spectroscopy. The observed spectrum showed clearly the effect of nuclear‐spin statistical weights, establishing the presence of a Cb2 axis in the molecule. The spin–rotation splitting was not resolved; only some high‐Ka lines were found broader than others, placing an upper limit for the eaa constant at about 200 MHz or less. The rotational constants derived from the observed spectrum indicate that the molecule is essentially planar. The C–C bond length and the CCC bond angle were calculated from the ground‐state rotational constants to be 1.3869 A and 123.96°, respectively, where structural parameters involving hydrogens were fixed to those of ab initio values.

Rydberg—valence mixing in the C 1s excited states of CH4 probed by electron spectroscopy

Abstract The C1s → n dt 2 Rydberg series and the ν = 1 vibrational levels of the symmetric mode ( ν 1 ) in the dominant C1s → n pt 2 series are clearly identified in the C 1s high-resolution electron-yield spectrum of CH 4 . In the resonance Auger electron spectra the participant Auger decay rate following the C1s → 3sa 1 , 3pt 2 and 3dt 2 excitations are 5.5%, 2.5%, and 3.7% of the total Auger decays, respectively, indicating that these Rydberg states do not have so strongly mixed valence character. The ordering of the valence contribution as 3sa 1 > 3dt 2 > 3pt 2 is consistent with the theoretical prediction.

Interatomic potentials of triplet s‐Rydberg series of HgNe and HgAr van der Waals dimers

The optical–optical double resonance (OODR) spectra of Rydberg 3Σ+ states of Hg(n3S1)Ne (n=8–10) and Hg(83S1)Ar were measured by using A and B states as intermediate states in the OODR process. The interatomic potentials of three states of HgNe and one state of HgAr were determined over a wide range of interatomic distance, R=3–7 A, by the analysis of the vibrational structure of their OODR spectra. It was found that the potential shape varies sensitively with n and converges to that of the ion core, HgNe+. Dissociation energies (De) of the Rydberg states for the n=8, 9, and 10 were derived to be 209(2), 284(2), and 309(2) cm−1, respectively. Using the quantum defect orbital [G. Simons, J. Chem. Phys. 60, 645 (1974)], which represents a hydrogenic radial wave function for a Rydberg state with a given quantum defect, was introduced to interpret the characteristic n dependence of the interatomic potential. It was shown that the interatomic potential for the Rydberg states can be expressed by the sum of the ...

Frustration of direct photoionization of Ar clusters in intense extreme ultraviolet pulses from a free electron laser

We have measured the kinetic energies of fragment ions from Ar clusters (average cluster size N~ 10?600) exposed to intense extreme ultraviolet free electron laser pulses (? ~ 61 nm, I~ 1.3? 1011 W cm?2). For small clusters (N 200), the average kinetic energy of ions strongly increases with increasing the cluster size, indicating a promotion of the multiple ionization, whereas the average kinetic energy is observed to be saturated for N 200. Considering how many photoelectrons can escape from the cluster, it was found that the size dependence of the ion kinetic energy exhibited the frustration of direct photoionization, which resulted from the strong Coulomb potential of the highly ionized cluster.

Ion-ion coincidence studies on multiple ionizations of N2 and O2 molecules irradiated by extreme ultraviolet free-electron laser pulses

We have investigated multiple ionization of N(2) and O(2) molecules by 52 nm extreme-ultraviolet light pulses at the free-electron laser facility SCSS in Japan. Coulomb break-up of parent ions with charge states up to 5+ is found by the ion-ion coincidence technique. The charge-state dependence of kinetic energy release distributions suggests that the electrons are emitted sequentially in competition with the elongation of the bond length.

Ion momentum spectroscopy of N2 and O2 molecules irradiated by EUV free-electron laser pulses

We have investigated dissociative ionization of N2 and O2 molecules by 52 nm extreme-ultraviolet light pulses at the free-electron laser facility in Japan. Distributions of kinetic energy release were measured at two different laser power densities below 3 × 1013 W cm−2 and intermediate and final states of the sequential two photon transitions were identified.

Auger electron spectra of CF3CN, CF3Cl, CF2Cl2 and CFCl3

Abstract The F KVV and Cl LVV Auger electron spectra of the chlorofluorocarbon molecules CF 3 Cl, CF 2 Cl 2 and CFCl 3 , as well as the F, N and C KVV Auger spectra of the CF 3 CN molecule, have been observed using electron-impact excitation. The spectra have been interpreted with the help of ab initio calculations for the local density of states. The fragmentations specific to the atomic site where the core hole is created, observed for these molecules, are discussed in connection of characters of the Auger final states analyzed in the present study.

Controlling Low-Energy Electron Emission via Resonant-Auger-Induced Interatomic Coulombic Decay.

We have investigated interatomic Coulombic decay (ICD) after resonant Auger decay in Ar2, ArKr, and ArXe following 2p3/2 → 4s and 2p3/2 → 3d excitations in Ar, using momentum-resolved electron-ion-ion coincidence. The results illustrate that ICD induced by the resonant Auger decay is a well-controlled way of producing energy-selected slow electrons at a specific site.

Collision induced absorption in mercury–rare-gas collisions

The far-wing excitation and probe technique is applied to observe quasimolecular absorption bands on the blue side of the Hg 6 1S0–6 3P2 atomic line for the Hg–Ar, Hg–Kr, and Hg–Xe mixtures. It is found that the excitation of this band is followed predominantly by a rapid elastic half-collision scattering on the excited state potential yielding the nascent product state Hg(3P2). This gives direct evidence of the assignment of the absorption to the c 31→X 10 collision induced dipole transition of the Hg–rare-gas quasimolecules. A chance of nonadiabatic transition from the c state is negligibly small compared to the elastic scattering. Analytical procedures are presented to deduce the c–X transition dipole moment from the relevant potential energy curves by making use of the Hund’s coupling schemes of the molecular electronic states. The c–X transition dipole moment is estimated as a function of the internuclear distance and is incorporated into the analysis of the observed band profiles. The potential ener...

Strong-field electron spectra of rare-gas atoms in the rescattering regime: enhanced spectral regions and a simulation of the experiment

We report experimental and theoretical laser-induced photoelectron spectra of Ne, Ar, Kr and Xe in the direction of the laser polarization at laser intensities in the region 0.5–3.2 × 1014Wcm−2. For Ar and Xe, spectra at different angles are also presented for the laser intensities of 2.4 × 1014Wcm−2 for Ar and 1.3 × 1014Wcm−2 for Xe. Resonance-like structures evolve as a function of the laser intensity in the longitudinal spectra, which become suppressed at large angles. The simulations are in the context of the strong-field approximation, which is augmented to account for rescattering and the atom-specific electron–positive-ion scattering potentials, and they include focal averaging as well as saturation. Agreement between the data and these simulations is generally fair, especially for intensities below the saturation regime.